Better to lose a few voters than to have some people voting several times. In Australia registration for voting, and voting itself, has been compulsory for many decades. You have to turn up at the polling station on voting day, even if you scribble "Blow the lot" on your voting paper.

Compulsory voting ensures everyone has the right to exercise the casting of their votes. People fought long and hard for their right to vote. What they do with that vote is also their right. If their resultant vote is void them they cannot exactly complain about the results.